It has already been known that a powdery high polymer of acetylene obtained by polymerizing acetylene with a Ziegler-Natta catalyst is a semiconductor material useful as electronics and electrical elements. It has also been known that when the powdery acetylene high polymer is treated with an electron acceptor compound, its electrical conductivity increases to 1,000 times at the highest, and when it is treated with an electron donor compound such as ammonia or methylamine, its electrical conductivity decreases to 1/10,000 at most [D. J. Berets et al., Trans. Faraday Soc. 64 823 (1968)]. However, the powdery acetylene high polymer used there is an assembly of non-fibrous microcrystals, and is essentially different in the form of molecular chains from the acetylene high polymer used in this invention which consists of fibrous microcrystals. Hence, it only gives molded articles of low mechanical strength, and the effect of improving its electrical conductivity is not entirely satisfactory.
Some of the inventors of the present invention already discovered and proposed a process for producing a film-like or fibrous acetylene high polymer having a fibrous microcrystalline (fibril) structure (Japanese Patent Publication No. 32581/73). The process for production according to this technique will be described hereinbelow. The film and fibers produced by this process are a crystalline high polymer in which fibrous microcrystals having a diameter of from 200 to 300 .ANG. are randomly oriented. This acetylene high polymer is a linear unsaturated hydrocarbon composed of a chain of cis or trans conjugated double bonds, and is possibly partially crosslinked. The configuration of the double bonds of the acetylene high polymer produced by this process differs depending upon the polymerization temperature. In a high polymer obtained by polymerization at -78.degree. C. or below, 98% of its double bonds are cis bonds. But as the polymerization temperature increases, the proportion of trans bonds increases, and a polymer obtained by polymerization at +150.degree. C. or higher consists almost entirely of trans bonds. When a high polymer containing cis bonds is heat-treated at 200.degree. C. for 30 minutes in vacuum or in an inert gas, it can be isomerized completely to a polymer consisting of trans bonds. By adjusting the treating temperature and time, a high polymer having a desired cis-trans ratio can be produced.
The electrical, mechanical and optical properties of this polymer vary greatly according to the cis-trans ratio. For example, the electrical conductivity at 25.degree. C. of the polymer is 1.7.times.10.sup.-9 ohm.sup.-1.cm.sup.-1 when its cis content is about 95%, and 4.4.times.10.sup.-5 ohm.sup.-1.cm.sup.-1 when its trans content is about 95%. The break strength of the polymer is 3.8 kg/mm.sup.2 when its cis content is 98%. It gradually decreases with increasing trans content, and is 2.4 kg/mm.sup.2 when its trans content is 96%. The break elongation of the polymer ranges from 140% at which the cis content is 98% to below 5% at which the trans content is 96%. Accordingly, a film-like or fibrous acetylene high polymer having a high cis content can be stretched by a mechanical operation to orient its fibrous microcrystals in the stretching direction, and therefore, a monoaxially oriented film-like or fibrous acetylene high polymer having a high cis content can be produced. When the monoaxially stretched acetylene high polymer is heated under mechanical tension to isomerize the cis bonds to trans bonds, its stretching proceeds further whereby a film-like or fibrous acetylene high polymer having a high trans content and being oriented to a higher degree can be produced.
It has already been reported that when the film-like or fibrous acetylene polymer produced by this process is doped with an electron acceptor compound, for example halogens such as Cl.sub.2, Br.sub.2, I.sub.2, ICl or IBr or arsenic pentafluoride, its electrical conductivity increases, and especially when the electron acceptor compound is arsenic pentafluoride, a highly conductive acetylene high polymer having an electrical conductivity of 560 ohm.sup.-1.cm.sup.-1 at the highest can be obtained [J. C. S. Chem. Commun. 578 (1977), Phys. Rev. Lett. 39, 1098 (1977), J. Am. Chem. Soc., 100, 1013 (1978), J. Chem. Phys. 69, 5098 (1978)].